Chemical vapor deposition apparatus for manufacturing semiconductor devices

ABSTRACT

There is provided a method of optimizing recipe of in-situ cleaning process for process chamber after a specific process on semiconductor wafers by using Residual Gas Analyzer Quadrupole Mass Spectrometer (RGA-QMS). According to the present invention, a Chemical Vapor Deposition (CVD) apparatus for manufacturing semiconductor devices comprises: a process chamber; process gas supply line for supplying process gas into the process chamber; a waste-gas exhaust line for removing the waste-gas from the process chamber after process; a supply line for supplying a CiF 3  gas into the process chamber; a sampling manifold for sampling the gas inside process chamber by using pressure difference; and RGA-QMS for analyzing the sampling gas, and the optimization of the end points according to gas flow, pressure, and temperature of the cleaning process for the process chamber is achieved through the analysis by above RGA-QMS.

FIELD OF THE INVENTION

The present invention relates to a Chemical Vapor Deposition apparatusfor manufacturing semiconductor devices, its driving method, and amethod of optimizing a cleaning process for the process chamber. Moreparticularly, the invention relates to in-situ cleaning of processchamber after processing of semiconductor wafers by using Residual GasAnalyzer Quadrupole Mass Spectrometer (RGA-QMA).

DESCRIPTION OF THE RELATED ART

Generally, the semiconductor device fabrication process is carried outinside a process chamber having certain pre-set process conditions. Inparticular, when a CVD (Chemical Vapor Deposition) process is performedon a semiconductor wafer, a layer of material is deposited not only onthe wafer, but also on the inner wall of the process chamber tube, andthe boat(s) for moving the wafers between the process chamber and aloadlock chamber where the wafers are stored. As these unwanted layersare repeatedly stressed during the loading/unloading of the wafers,particles are released into the chamber that can cause defects on thewafer during the fabrication process.

In order to reduce the causes for defects, PM (Preventive Maintenance)is repeatedly conducted to clean the process tube at regular intervals,but the productivity of semiconductor devices is decreased due to theinterruption of the process line operation.

FIG. 1 illustrates a conventional PM sequence for a general processtube. First, the system is cooled down after carrying out a specificprocess on semiconductor wafers. After the process chamber is completelycooled, the tubes of the process chamber are taken out one by one so asto carry out wet-etch cleaning of the tubes. The wet-etch generally useschemicals such as HF group in order to remove a polysilicon film or asilicon nitride film from the inside of the process tube. Then, theremoved tubes are assembled inside the process chamber and a vacuum testis performed. Process Recertification is carried out to see if theprocess chamber is ready for a new process and if the process conditionsfor the next process are substantially set up therein.

However, the above PM process represents considerable efforts andexpenses, and takes over 24 hours to complete. Therefore, in order toovercome the problems, a plasma etch of using NF₃ and CF₄ gas is carriedout instead of the wet-etch. Alternatively, Thermal Shock Technology isused for removing the layers formed by thermal stress inside thechamber, or the chamber is dry-etch using ClF₃, BrF_(5.)

However, even though these technologies are employed, the tubes stillmust be removed and reassembled and the expense, the labor, and downtimeremain as problems.

SUMMARY OF THE INVENTION

The present invention is directed to provide a CVD apparatus formanufacturing semiconductor devices wherein a process chamber isequipped with cleaning gas supply line, a sampling manifold, and a gasanalyzer which are used to clean the tubes in situ. As a result, themethod of the present invention substantially obviates one or moreproblems, disadvantages, and limitations of prior art.

Another object of the present invention is to provide a method ofdriving the CVD apparatus, wherein a specific process is performed onwafers, and then in-situ cleaning is performed inside a process chamber,after semiconductor wafers are unloaded.

Another object of the present invention is to provide a method ofoptimizing a cleaning process for a process chamber.

To achieve these and other advantages and in accordance with the purposeof the present invention as embodied and broadly described, a CVDapparatus of the present invention includes a process chamber in which adeposition process for manufacturing semiconductor devices is carriedout; a plurality of process gas supply lines for supplying process gasesto the process chamber; a waste-gas exhaust line for removing thewaste-gas from the process chamber; a cleaning-gas supply line forsupplying a cleaning gas to the process chamber; a sampling manifoldconnected to the process chamber for sampling the gas inside therein byusing pressure difference; and a gas analyzer for analyzing the samplinggas from the sampling manifold.

Preferably, the process chamber is a Low Pressure Chemical VaporDeposition (LPCVD) chamber having a sealed outer tube and an inner tubehaving an open top inside the outer tube. The cleaning gas is CIF₃. Thecleaning-gas supply line is connected to the inner tube, and thesampling manifold is connected to the outer tube. An orifice isinstalled in the sampling manifold such that the pressure therein ismaintained at the same pressure as in the process chamber. The samplingmanifold comprises a first air valve, a second air valve, a firstisolation valve, a second isolation valve, a third isolation valve, anda gate valve between the connecting point with the outer tube. Apurge-gas supply line is also provided in the sampling manifold. Thepurge-gas supply line of the sampling manifold is connected to the firstair valve and the second air valve respectively from the purge gassupply source, and third and a forth air valves are further providedbetween them respectively. A Capacitance Manometer (CM) gauge and asampling pump are preferably installed between the first isolation valveand the second isolation valve of the sampling manifold in order tocontrol the first pressure of the sampling manifold.

A scrubber is provided for receiving and cleaning the waste-gas passingthrough the waste-gas exhaust line, and the gas sampling line.

The gas analyzer is preferably a RGA-QMS(Residual GasAnalyzer-Quadrupole Mass Spectrometer) comprising a mass-analyzer, aturbo pump, and a baking pump, which is preferable in the aspect ofenvironmental protection.

The invention is also embodied in a method of driving a CVD apparatusfor manufacturing semiconductor devices. The CVD apparatus includes: aprocess chamber; a plurality of process gas supply lines for supplyingprocess gases into the process chamber; a waste-gas exhaust line forremoving the waste-gas from the process chamber after processing; acleaning-gas supply line for supplying a cleaning gas to the processchamber; a sampling manifold connected to the process chamber; and a gasanalyzer for analyzing the sampling gas from the sampling manifold. Themethod comprises the steps a) sampling the gas from the process chamber;b) outgasing while baking the gas in order to reduce the initialbackground of the gas analyzer below a certain value; c) conducting acontamination analysis of each of the process gas supply lines; d)performing a specific process for the semiconductor wafers contained inthe process chamber) unloading the wafers after the above specificprocess is completed, and exhausting the waste-gas from the processchamber; and f) cleaning the inside of the process chamber by supplyinga cleaning gas thereinto.

The sampling manifold and the gas analyzer are continuously purged witha purge gas before conducting the sampling to ensure the precision ofthe gas analyzer. The contamination analysis for the process gas supplyline is performed by passing nitrogen gas through each isolated processgas supply line and checking for leakage. Preferably, the fabricationprocess of semiconductor wafers is the one for forming asilicon-containing layer on the wafer, and the cleaning process isconducted by introducing nitrogen gas and ClF₃ gas as cleaning gaseswhile maintaining uniform pressure and inside the process chamber sothat the end point of the cleaning process is easily detected.

The method further comprises a step of measuring particles inside theprocess chamber before and after the cleaning process, and the step ofmeasuring metal/ion contaminants inside the process chamber before andafter the cleaning process so as to determine the effectiveness of thecleaning process.

To achieve still another object of the present invention, a method ofoptimizing the cleaning process for a process chamber, the cleaningprocess carried out in-situ after a specific process is performed for awafer placed inside the process chamber, with a cleaning gas supply linefor supplying the cleaning gas into the process chamber, a samplingmanifold connected to the process chamber, and a gas analyzer foranalyzing the sampling gas from the sampling manifold. The methodcomprises: a) after performing a specific process on the semiconductorwafer, cleaning the process chamber by supplying a certain amount ofnitrogen gas and ClF₃ as cleaning gas while maintaining a constantpressure and temperature inside the process chamber until the cleaningend point by the gas analyzer; and b) after performing the same specificprocess for another semiconductor wafer, cleaning the process chamber bysupplying a certain amount of nitrogen gas and CIF₃ as cleaning gas, andvarying the pressure and the temperature inside the processing chamberuntil the cleaning end point by the gas analyzer.

Preferably, the end point of the gas analyzer is determined by theintersecting point of amplified traces for an etch gas and the etchingbyproducts.

According to the present invention, when a specific process is performedon a semiconductor wafer and the cleaning process is carried out insidethe process chamber by using CIF₃ gas, the mechanism is exactlymonitored, and the composition of the cleaning process is optimized tosimplify the process and to improve process efficiency.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a brief representation showing the conventional sequence of acleaning process for the process tube of the conventional Chemical VaporDeposition (CVD) apparatus for manufacturing semiconductor devices;

FIG. 2 is a schematic representation showing the CVD apparatus formanufacturing semiconductor devices according to one embodiment of thepresent invention;

FIG. 3 shows a sequence for the process analysis and the cleaningprocess in the CVD apparatus of FIG. 2 according to one embodiment ofthe present invention;

FIG. 4 shows an analysis trend for the storage polysilicon depositionprocess according to one embodiment of the present invention;

FIG. 5 shows an analysis trend for the cleaning process according to oneembodiment of the present invention;

FIG. 6 is a graph correlating etch rate in the cleaning process topressure inside a process chamber according to one embodiment of thepresent invention;

FIG. 7 is a graph correlating etch rate in the cleaning process totemperature inside a process chamber according to one embodiment of thepresent invention; and

FIG. 8 is a graph correlating etch rate in the cleaning process to CIF₃flow inside a process chamber according to one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 2 is a schematic representation showing the CVD apparatus formanufacturing semiconductor devices according to one embodiment of thepresent invention. A process chamber 10 comprises an outer tube 14 andan inner tube 16. Inside the process chamber 10, various processes suchas deposition process, plasma process, diffusion process, or CVDprocess, etc. are performed. A loadlock chamber 12 is installed belowthe process chamber. A boat 18 for holding wafers to be processed ismoved up and down between the process chamber 10 and the loadlockchamber 12 by an elevator 20. A gas supply line 22 for supplying processgas for processing is connected to the lower side of the inner tube 16.The gas supply line 22 may have a separate pipe line and valve for eachprocess gas or cleaning gas. In the system shown in FIG. 2, individualprocess gas supply lines and valves 32,34,36,38,40 are provided for SiH₄supply source 24, PH₃ supply source 26, N₂ supply source 28, and ClF₃supply source 30 respectively. The CIF₃ supply source 30 is a cleaninggas supply source, which will be mentioned below. The gas supply line 22may have a separate pipe line for each process gas or cleaning gas.

Meanwhile, the process waste-gas is evacuated from outer tube 14,through a discharge line 42, by a discharge pump 44, and is then routedto scrubber 46 for cleaning.

In order to monitor the gas composition inside the process chamber 10, asampling port 48 is installed in the outer tube 14, The sampling port 48is connected to a sampling manifold 50, preferably by using a flexibleconnecting line 52. Sampling line 54 of sampling manifold 50 is made of⅓ inch diameter electropolished stainless steel pipe. Flow throughsampling line 54 is controlled by a first air valve 62, a second airvalve 66, a first isolation valve 68, a second isolation valve 70, athird isolation valve 72, and a gate valve 74. The first isolation valve68 and the second isolation valve 70 are each fitted with a 100 micronorifice; and the third isolation valve 72 is fitted with a 250 micronorifice.

The sampling manifold 50 has an N₂ supply source 56 for use as a purgegas, which is available whether or not samples are being drawn. Thevacuum system can be damaged by the concentration of the gas due to asmall amount of water inside the Gas Distribution System (GDS) so thatit is very important to precisely control the purge cycle or cleaningtime for the process chamber. The N₂ 58 is connected to the first airvalve 62 and to the second air valve 66. Further, a CM gauge 76 isinstalled between the first isolation valve 68 and the second isolationvalve 70 on sampling line 54. Sample line line 54 is connected tosampling pump 90, which discharges to the scrubber 46.

Meanwhile, sampling line 54 is connected to a gas analyzer 80 throughgate valve 74. The gas analyzer 80 uses a commercially available RGA-QMS(Residual Gas Analyzer-Quadrupole Mass Spectrometer 84. An ion gauge 82is installed on the mass analyzer 84. Sample gases pass through a turbopump 86 and a baking pump 88, and to the scrubber 46

Meanwhile, the ClF₃ gas for use in the present invention is a cleaninggas that can be also used in the cleaning of polysilicon, siliconnitride, silicon glass, and tungsten silicide. It can be used in the lowtemperature state as well as plasma state, and has the excellentchemical selectivity so that it performs etching at the portions whereplasma cannot reach. It also has the advantage that it is highlyunlikely to generate particles that could contaminate the wafer surface.In use ClF₃ is generally diluted to a concentration of 20+5 volume %with an inert gas such as N₂. While the lower pressure in the processchamber is good for the uniform etch for the layer inside the chamber,the higher mixing rate of etch gas is good for increasing the etch rate.It is preferable to heat the process chamber to a temperature higherthan the boiling point of the ClF₃, prior to the introduction of CIF₃and preferably higher than 400° C. for the desirable etch rate. SinceClF₃ is a very reactive gas, if the etch rate is too high, tubes 14 and16 could also be etched, shortening the useful life of the tube.

The ClF₃ supply pipe is preferably formed of nickel, monel, hastelloy,316L stainless steel, or a polymeric material due to the properties ofthe ClF₃.

Meanwhile, the RGA-QMS (Residual Gas Analyzer-Quadrupole MassSpectrometer) used as the gas analyzer 80 is operated in such a mannerthat sampled gas from the process chamber is ionized by bombardment withelectrons accelerated with 70 eV. Then, Quadrupole Mass Spectrometerpasses only those ions having a specific rate of mass to electriccharges so as to obtain a mass spectrum. By the composition of the ionsachieved from the above results, the composition of the sampled gas canbe determined. The RGA-QMS used in the present invention is a portablesystem, and unlike general Open Ion Source (OIS) used in the sputteringprocess, the ion source is a Closed Ion Source (CIS) so that it ispossible to analyze the process gas as well as bulk gas.

The sampling pressure is controlled uniformly below the process chamberpressure by the orifices (100/250 micron) inside the sampling manifold50.

Turning now to FIG. 3, a sequence for the process analysis and thecleaning process in the CVD apparatus of FIG. 2 will now be described.First, gas analyzer 80 is connected to the sampling manifold. N₂ gas iscontinuously supplied to purge the RGA-QMS. First air valve 62 and thirdair valve 60 are closed; second air valve 66 and fourth air valve 64 areopened. Then, fourth air valve 64 is closed, and first air valve 62 isopen, and the gas inside the process chamber 10 is sampled. At thisstage, if it is necessary to control the pressure both in the processchamber 10 and the sampling line 54, it can be done by operating asampling pump 90 based on the pressure indicated on a CM gauge 76.

Then, the RGA-QMS baking evaluation is conducted. That is, after placinga quadrupole mass spectrometer inside an RGA-QMS chamber (not shown),baking is carried out in order to decrease the background. Since RGA-QMSis very sensitive to contamination, its contamination level isdetermined by analyzing the background spectrum as part of every test tomeasure contamination if any, by water and oxygen. When thecontamination level is high, the RGA-QMS chamber is baked at about 250°C., and the sampling manifold is baked at about 150° C. so as to reducethe contamination level. During baking, the partial pressure of eachmolecular contaminant (H₂O, H₂, O₂, Ar, CO₂, etc.) is monitored. Theoutgasing of the contaminants is accelerated through the baking so thatthe background of the RGA-QMS is reduced.

Sequentially, the contamination for the gas line is analyzed, in orderto analyze the integrity of each supply line (SiH₄, PH₃, and N₂). N₂ gasat 500 SCCM is introduced into each supply line, one by one. Gas insidethe process chamber is then sampled and analyzed to determine if the gassupply line is leaking.

Then, a specific process for semiconductor wafers is carried out, andsampling is carried out so as to analyze the process. At this time, forexample, in a storage-polysilicon deposition step of DRAM processing,continuous sampling may be carried out in the prepurge and after-purgestep as well as in the deposition step. The manifold is maintained belowthe 0.9 Torr, pressure of the process chamber, by way of the criticalorifice on the sampling manifold of the RGA-QMS. FIG. 4 shows a typicalanalysis trend for the storage-polysilicon formation process.

After the specific process for semiconductor wafers is completed, theboat containing the wafers is unloaded from a process chamber, and thewaste-gas therein is discharged. Then, a ClF₃ in-situ cleaning processis carried out. In the case of depositing storage-poly layer to athickness of 48,000 Å, the adhered layer inside the process chamber isetched away using a mixture of 2800 SCCM N₂ gas and 700 SCCM ClF₃ gas.

Then, cleaning process steps are analyzed to determine the End PointDetection (EPD) of cleaning process. The cleaning process is analyzed byalternately varying the pressure and temperature of the process chamberwhile maintaining the flow of cleaning gas (for example, N₂ gas of 2800SCCM, and ClF₃ gas of 700 SCCM). Like the storage-poly formation processanalysis, the EPD analysis of the cleaning process is performedthroughout the whole cleaning process. FIG. 5 shows an analysis trendfor the in-situ cleaning process by ClF₃ after storage-poly depositionprocess. As shown in FIG. 5, the cleaning process is divided into 3steps. The first step is evacuating and purging the chamber prior tocleaning, as shown in FIG. 5, during the SCCM time from 0 to 50. TheClF₃ etching is carried out in the second step, and is represented inFIG. 5 from 50 to about 280 scan. The third step is the evacuation andpurging after the etching is complete, which corresponds to the timeafter 280 scan.

As shown in FIG. 5, the EPD of the cleaning process is the point 100around 280 scan. At about point 100 (scan=280), the concentration of HF+equals the concentration of SiF₃+ in the process chamber. At that point,the ClF₃−N₂ gas mixture has largely etched away the silicon-containinglayers on the inside walls of process chamber 10. After that point,continued flow of etchant gas into the process chamber results inunwanted etching of the polysilicon layer by the fluoride and chlorideradicals generated by ClF₃. The unwanted etching of the polysiliconlayer is indicated, according to the invention, by the detection of HF.HF is a polysilicon etching byproduct that is not present in relativelyhigh concentrations during the etching of silicon from the processchamber walls. By repeatedly carrying out the same storage-polydeposition process by varying the pressure and temperature of processchamber 10, the flow rate of the ClF₃, and determining EPD for eachcase, the process time for each step of the cleaning process can beoptimized. The results of the optimization as above are shown in FIGS.6, 7 and 8. FIG. 6 is a graph correlating etch rate in the cleaningprocess to the pressure inside a process chamber 10. FIG. 7 is a graphcorrelating the etch rate during the cleaning process to the temperatureinside process chamber 10. FIG. 8 is a graph correlating etch rate inthe cleaning process to ClF₃ flow rate inside a process chamber. Theeffectiveness of the cleaning can be evaluated by monitoring theparticles present in process chamber 10 before and after the cleaningprocess. Metal and ion contaminants such as Fe, Cr, Ni, Zn, Ti, S, Cl,F, NH₄ can also be monitored using with TXRF/HPIC (Total X-rayReflection Fluorescence/High Performance Ion Chromatography) before andafter the cleaning process.

Therefore, according to the present invention, without removing theprocess tubes, the process chamber can be in-situ cleaned so that thelife of process chamber is increased, the cleaning time is shortened,and productivity is improved.

In addition, according to the present invention, the in-situ cleaningprocess can be optimized so that the life of the process chamber isincreased and cleaning time is shortened. Further, according to thepresent invention, the processes for the wafers continuously ismonitored, and analyzed so that the process malfuctioning is preventedcontributing to the increase of the productivity. Still further, whilethe present invention has been described in detail, it should beunderstood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims.

What is claimed is:
 1. An apparatus for manufacturing semiconductordevices, comprising: a semiconductor process chamber; a plurality ofprocess gas supply lines connected to the process chamber; a waste-gasexhaust line connected to the process chamber and a pump; a cleaning-gassupply line connected to the process chamber; a sampling manifoldconnected to the process chamber, wherein the sampling manifoldincludes: a first portion at a first pressure which is substantiallyequal to a pressure within the process chamber; a second portion at asecond, lower pressure; and a member defining an orifice separating thefirst and second sampling manifold portions; and a gas analyzerconnected to the sampling manifold, wherein said cleaning-gas supplyline supplies cleaning gas to the process chamber and said gas analyzerdetermines when to stop supplying the cleaning gas thereto.
 2. Theapparatus of claim 1, wherein the sampling manifold includes a first airvalve, a second air valve, a first isolation valve, a second isolationvalve, a third isolation valve, and a gate valve.
 3. The apparatus ofclaim 2, wherein the sampling manifold includes a purge-gas supply line.4. The apparatus of claim 2, wherein the purge-gas supply line of thesampling manifold is connected to the first air valve and the second airvalve, and wherein third and fourth air valves are further providedbetween the first and second air valves.
 5. The apparatus of claim 2,wherein a Capacitance Manometer (CM) gauge and a sampling pump areinstalled between the first isolation valve and the second isolationvalve of the sampling manifold.
 6. The apparatus of claim 5, wherein ascrubber is further installed for cleaning the waste-gas passing throughthe pumping means of the waste-gas exhaust line, and the gas passingthrough the sampling pump is exhausted through the scrubber.
 7. Theapparatus of claim 2, wherein orifices of the first isolation valve, thesecond isolation valve, and the third isolation valve of the samplingmanifold are 100 micron, 100 micron, and 250 micron respectively.
 8. Theapparatus of claim 1, wherein the gas analyzer is an RGA-QMS (ResidualGas Analyzer-Quadrupole Mass Spectrometer) comprising a mass-analyzer, aturbo-pump, and a baking pump.
 9. The apparatus of claim 8, whethercomprising a scrubber for cleaning waste-gas and connected to waste-gasexhaust line and the gas analyzer.
 10. The apparatus of claim 1, whereinsaid gas analyzer determines when to stop supplying the cleaning gas bycomparing the concentration of HF⁺ and SiF₃ ⁺ ions.